Dielectric stencil



June 20, 1950 A. R. LINDSAY DIELECTRIC STENCIL Filed Sept. 25, 1948V//MWM// l7 JN V ENTOR.

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Patented `une 20, 1950- DIELECTEIC STENCIL Allen R. Lindsay, ClevelandHeiglts, Ohio Application September 23, 1948, Serial No. 50,757

4 Claims. (CI. lol- 1282) This invention relates to a dielectric stencilfor use with an electrical etching device such as is used for markingvarious types of metallic articles such as tools, machines and variousparts thereof.

In devices of this kind the stencil has portions thereof depressed inthe form of the character desired. The stencil is then secured to asuitable etching tool and in operation the stencil is brought intocontact with the work to be marked and the depressions are filled with asuitable elec- Then an electric current is passed through theelectrolyte to the work, the stencil holder or tool acting as thecathode and the work constituting the anode. Such an etching tool isshown in my co-pendng application Serial No. 631A01, filed November 28,1945, and now issued as Patent No. 2,498,129 granted Sept. 2, 1949. Theactual etching time is very short, just a few seconds, so that a verylarge number of articles a;

can be marked in a short time. As the stencil is repeatedly brought intoengagement with the work, which very often has a rough surface, itquickly wears out and has to be frequently replaced which consumesconsiderable time and many stencils.

The principal object of the invention is to provide a dielectric stencilfor use with electrical etching devices that is so constructed that itwill have a much longer life and can be used a great many more timesthan previously known stencils of this character.

Another object of the invention is to provide a stencil of thischaracter which will produce a clear-cut, well-defined mark upon ametallic article.

Another object of the invention is to provide a stencil possessing theaforesaid characteristics which is easily and economically manufacturedand is very efcient in operation.

Other and more limited objects of the invention will be apparent fromthe following specication and the accompanying drawings forming a partthereof wherein:

Fig. 1 is a side elevation of a stencil constructed according to myinvention;

Fig. 2 is 'a bottom plan View thereof; and

Fig. 3 is a greatly enlarged fragmentary section taken on the line 3-3of Fig. 2.

Referring now to the drawings by reference characters, the numeral lindicates generally my improved stencil which as illustrated hereincomprises a bottom 2 and an annular wall 3 integral with the bottom 2.The upper end of the annular wall 3 is fiared outwardly as indicated at4. The

character to be etched is indicated at 5, which as illustrated is thenumeral I. Although I have illustrated my improved stencil as generallycircular in shape, it will be obvious to anyone skilled in this art thatit can be square, rectangular or any other desired shape depending onthe character .and. shape or size of the mark desired and on the type ofetching tool With which the stencil is to be used. Also the stencil neednot be cup shaped as shown. In some instances it may be desirable tohave the stencil in .the form of a flat sheet.

The stencil is made from a composite sheet of material 6 which is firstmolded into the desired shape, after which the desired character ispressed into the bottom 2 by a suitable die.

The material 6 comprises a treated paper sheet i, a thin film of wax 8and a thin layer of high temperature paraflin and buna rubber 9 allfirmly bonded together into a composite sheet. The

paper 'I is preferably uncoated long fibre paper having extremely opentissues, which has been treated with chlorinated oil to seal thehygroscopic fibres and bond them together. The paper is very pervious sothat electrolyte can readily pass through. A wax solution is applied toone side of the paper by passing the paper over a chilled roller whichclips into a bath of the heated 'wax solution. The wax solutioncomprises parafin and beeswax, or other animal wax, which have beendissolved in ether or other suitable solvent and heated to approximatelyF. When the solution cools and dries, it forms the thin wax film 8 whichis firmly bonded to the paper l. An emulsion of high temperatureparaffin and buna rubber is then spray coated on the film of wax 8 by ahot blast air gun. As the emulsion comes into contact with the wax film8` it solidifies forming the outer layer 9 of the stencil material 6. Inpreparing the paraffin and buna emulsion F. parafiin is melted anddissolved in mineral ether and then heated to approximately 200 F. Thebuna rubber is dissolved in acetone and ether, and then the hot parafinsolution is added progressively in minute quantities to the bunasolution while the buna solution is being Violently agitated. Thisproduces a stable creamy emulsion.

After the stencil has been molded to the desired shape the desiredcharacter is impressed therein by forcing a suitable die into the outerface of the stencil. As the die is forced into the material it rupturesthe buna film 9 and displaces the wax and buna films 8 and 9 andcompresses the paper 'I as indicated at ID in Fig. 3. The dis- 'placedbuna and wax films form a. raised border around the character asindicated at H. As the die is pressed into the composite sheet 6 to formthe desired character the buna film 9 is first ruptured and the waX filmis softened. Further pressure displaces the wax film 8 and the buna film9 from under the die, leaving the paper sheet 1 eXposed as shown in Fig.3. The pressing of the die into the composite sheet also compresses, butdoes not rupture, the paper sheet 'I forcing out ali oil and Wax fromunder the compressed portion thereby providing a section through whichelectrolyte can readily pass. If the wax film 8 was not provided betweenthe paper sheet 'l andthe buna film 9 it would be very difiicult, if notimpossible, to r-upture and displace the buna film r The First,

uncoated long fibre open tissue paper which has been treated withchlorinated oil to seal the hygroscopic fibres and bond them together, afilm containing animal wax bonded to the outer side of said sheet, asecond film containing synthetic rubber bonded to said first mentionedfilm, an impression in said sheet defining a character to be etched,said films being perforated by said impression, and said second filmbeing displaced to provide a raised border around said impression.

2. A dielectric Stencil comprising a sheet of uncoated long fibre opentissue paper, a film containing animal wax bonded to the outer side ofsaid sheet, a second film containing synthetic rubber bonded to saidfirst mentioned film, an

- impression in said sheet defining a character to it helps tostrengthen the paper sheet 1, which in its natural state is veryweak;and second, permits the rupturing and displacement of the buna film 9without rupturing the paper sheet 1. After the character has beenimpressed in the Stencil the depression is filled with electroiyte andan electric current is passed through the electrolyte. This generatesenough heat to cure and yulcanize the rubber film forming the 'Walls !2of the depression and the raised border ll therea'ound. This gives therubber high mechanical strength and provides a tough tenacious filmwhich resists mechanical abrasion. The curing of the rubber film isgeneraily accomplished by attaching the Stencil to an etehing tool andusing it once `or twice to mark some .article.

In practice it has been found that a `Stencil constructed in this mannercan be used 1900 times before it is worn beyond :a desirable usagepoint.

Other known stencils when used in the same manner averaged only 30times.

From the foregoing it will be apparent to those skilled in this art thatI have provided a Very simple and efiicient device for accomplishing theobjects of my invention.

It is to be' understood that I am not restricted `to the particularconstruction shown and described herein as various modifications can he'made therein within the scope of the appended claims.

Having .thus described my invention, I-- claim:

1. A dielectric Stencil comprising a' sheet of rubber bonded to saidfirst mentioned film, an

:impression .in said sheet defining ta character to be etched, said.films being perforated by said impression.

4. A dielectric .Stencil 'compri sing ;a sheet of uncoated long fibreopen tissue paper, a :film containing 'animal waxbonded to the outerside of said sheet, a .second. film containing synthetic rubber bonded.to said first mentioned film, an impression in said .sheet defining a.character to be -etched, said films being .perforated by saidimpression.

ALLEN R. LINDSAY.

CES CITED The foliowing references 'are of record in th file 'of thispatent:

UNITED STATES PATENTS 'Number Name Date 1,293,983 Thomas Feb.. 11, 19191,37,1.57 Gestetner i VMar. 8, 1921 1 633972 Davis June 21, 19272,'14O,5D6 aGanning Dec. 20, '1938 &405,-508 Lindsay .Aug. 6, 19446

4. A DIELECTRIC STENCIL COMPRISING A SHEET OF UNCOATED LONG FIBRE OPENTISSUE PAPER, A FILM CONTAINING ANIMAL WAX BONDED TO THE OUTER SIDE OFSAID SHEET, A SECOND FILM CONTAINING SYNTHETIC RUBBER BONDED TOS AIDFIRST MENTIONED FILM AN IMPRESSION IN SAID SHEET DEFINING A CHARACTER TOBE ETCHED, SAID FILMS BEING PERFORATED BY SAID IMPRESSION.